The technical part of the profession of an optician consists in mounting a pair of ophthalmic lenses in or on a frame selected by the wearer.
This mounting comprises two main operations:                centering each lens, which consists in positioning and orienting the lens appropriately relative to the eye of the future wearer; and then        shaping each lens, which consists in machining or cutting its outline to the desired shape, taking account of the defined centering parameters.        
The present invention relates to the second operation of “shaping”. Shaping a lens to enable it to be mounted in or on the frame selected by the future wearer consists in modifying the outline of the lens so as to match it to the frame and/or to the desired lens shape. Conventionally, shaping comprises two main operations: an edging operation (or “roughing-out” operation); and a finishing operation that is adapted to the type of frame. Shaping consists in eliminating an unwanted peripheral fraction of the ophthalmic lens in question so as to bring its outline, which outline is usually initially circular, down to the arbitrary outline of the rim of the eyeglass frame in question or merely to the desired shape of pleasing appearance when the frame is of the rimless type. This shaping operation is usually followed by a chamfering operation that consists in rounding or chamfering the two sharp edges of the edged lens. The finishing operation depends on the way mounting is to be performed. When the frame is of the rimmed type, chamfering is accompanied by beveling which consists in forming a rib generally referred to as a bevel. The bevel is designed to engage in a corresponding groove, commonly referred to a bezel, that is formed in the rim of the eyeglass frame in which the lens to be mounted. When the frame is of the rimless type, the shaping of the lens and optionally the rounding (chamfering) of its sharp edges is/are followed by drilling the lens appropriately so as to enable the side branches or “temples”, and the nose bridge of the rimless frame to be fastened there to. Finally, when the frame is of the nylon string type, chamfering is accompanied by grooving that consists in forming a groove in the edge face of the lens, which groove is to receive the nylon string of the frame for pressing the lens against the rigid portion of the frame.
Usually, these operations are performed one after another on a single machine tool or grinder that is fitted with a set of appropriate grindwheels. Drilling can be performed on the grinder, in which case it is fitted with the corresponding tool, or else it is performed on a distinct drilling machine.
The operations of shaping and finishing can themselves be subdivided into a plurality of sub-operations, for example: roughing out, finishing, and polishing.
Usually, the lens is shaped on a numerically controlled grinder that possesses means for holding and driving the lens in rotation together with a plurality of grindwheels that are appropriate for the various operations to be performed. The lens is initially blocked on the holder-and-drive means in a known configuration such that its optical frame of reference is known, thereby enabling the operations to be performed accurately relative to said frame of reference. It will be understood that such blocking, accompanied by storing the optical frame of reference in a memory, serves to define and physically identify on the lens a geometrical frame of reference specifying characteristic points and directions of the lens, as are needed for matching it with the position of the pupil, together with shaping values so that the characteristic points and directions are properly positioned in the frame.
Recently, a new type of lens has become available on the market in which holding and driving difficulties have arisen. In order to limit dirtying of the faces of ophthalmic lenses, in particular for anti-reflection lenses, it is known to apply a specific coating to one or both faces of the lens, which coating is said to possess “low surface energy”. Such specific coatings have the feature of preventing adhesion of water (water-repellent coating) or of grease (oil-repellent coating).
Unfortunately, such coatings make the surfaces of the lens on which they have been deposited very slippery. The adhesive used for placing the centering-and-drive pad then adheres weakly to the slippery face of the lens. The same problem arises when applying blocking chucks that adhere weakly to the faces of the lens. While shaping the lens, the grindwheels that are removing material exert generally circumferential forces (friction forces) on the edge face of the lens, thereby generating high torque on the lens, in particular during roughing out of the lens during which a large quantity of material is ground away. As a result, during shaping, in particular during roughing out, the lens slips relative to the means for holding and turning the lens (the pad or the chucks). The centering of the lens, and in particular the orientation of its axis (i.e. the angular orientation of the lens in the frame of reference of the grinder) is then modified and the outline obtained for the lens differs, relative to its own optical frame of reference, from the final outline desired after shaping.
One solution consists in reducing the quantity of material that is removed on each grinding pass so as to reduce the torque exerted on the edge face of the lens. However that solution does not give satisfaction, and in any event significantly lengthens cycle times.
For blocking the lens with a pad, it is also known to apply an interface on the slippery coating so as to increase adhesion with the adhesive used for placing the pad. That solution does not give full satisfaction either, and overall it lengthens production throughput rates.
A similar problem arises when shaping lenses of thickness and material that make them fragile and that expose their coatings to a risk of cracking. It can be understood that a lens of small thickness made of a material that is deformable, such as polycarbonate, deforms in bending while it is being clamped between the support and rotary drive shafts of the shaper machine. Such deformation of the lens can reach excessive levels, leading to cracking of the coatings on the lens, which is unacceptable and causes the lens to be discarded. To avoid that phenomenon, it is necessary to reduce the deformation of the lens, and for this purpose to reduce the magnitude of the force clamping the lens between the support and rotary drive shafts of the shaper machine.
Furthermore, when subjected to machining, certain organic materials that are used in the composition of lenses give off substances that are smelly. This applies in particular to organic materials having medium and high refractive indices, typically indices greater than 1.6. It can readily be understood that giving off such smells is harmful, not only for the working conditions of operators acting on or near the shaper machines, but also in terms of client satisfaction when the workshop for preparing lenses for mounting is close to a sales area or is merely being visited.
Another problem arises when it is desired to shape a lens around an outline of sophisticated shape, in particular a shape presenting one or more concave portions which, seen in the mean plane of the lens, presents points of inflection. Under such circumstances, the shape generally cannot be obtained using a conventional tool for machining the periphery of the lens, such as a grindwheel or a bladed cutter, since the conventional tool is of a diameter that is too great to comply with the points of inflection.